The present invention relates to vehicle control systems, and in particular to methods and systems for detecting the presence of a minispare tire and suspending detection during braking.
Minispare tires are an alternative to full-sized spare tires in vehicles. The minispare tire is typically smaller, weighs less, and has a higher inflation pressure than a regular tire and, when installed in place of a damaged conventional tire, is sufficiently durable to allow the vehicle to travel to a nearby service station for assistance.
While minispares have a number of positive attributes, their smaller dimensions and higher inflation pressure compared to standard tires, can alter the performance of a vehicle's electronic stability control (ESC) system, traction control system (TCS), or antilock braking system (ABS). Therefore, vehicles include sensors or other devices to detect the presence of a minispare tire, so that appropriate corrections to the vehicle controls can be made to account for the presence of the minispare tire. Detection of a minispare tire is performed on a continuous basis, for example, by measuring the relative speeds of the wheels on the vehicle. Due to the smaller circumference, a minispare tire will have a greater rotational velocity than standard-sized tires at a given vehicle speed. Thus, if one wheel has a significantly higher rotational velocity than the others, it is assumed that a minispare tire is present and appropriate corrections are made in the vehicle control systems (e.g., ESC, TCS, and ABS).
However, detection of minispare tires is temporarily suspended when the vehicle's brakes are applied, in part because one or more tires including the minispare could slip during braking, which could lead to increased detection times or possibly inaccurate wheel-speed measurements. This is a particular problem on surfaces with a low coefficient of friction (low-p surfaces) such as ice or wet pavement.
One method that has been used to detect whether the vehicle's brakes are being applied is to determine whether the brake light switch (BLS) has been activated. The BLS is directly coupled to the brake pedal itself and responds to minimal movement of the pedal, even before any hydraulic pressure is built up in the braking system. When the BLS is activated the vehicle's control systems suspend minispare detection.